Wireless communication device and wireless communication method

ABSTRACT

The transmission of a reference signal, such as a CSI-RS, is enabled while maintaining a power saving effect when performing inter-cell cooperative transmission/reception or the like in a plurality of cells. In order to realize inter-cell cooperative transmission/reception, a CSI-RS which is used for estimating the state of a spatial propagation path of a communication line is generated by a CSI-RS generation unit, and the CSI-RS is disposed in a predetermined subframe by a disposition unit and transmitted. At this time, when a frame has ten subframes #0 to #9, the CSI-RS is disposed in the subframes #4 and #9, which are subframes excluding the subframes #0 and #5 incapable of transmitting a CSI-RS and are subframes other than subframes capable of acting as MBSFN subframes when discontinuous communication (Extended Cell DTX) is performed so as to achieve power saving, and transmitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 16/008,184filed on Jun. 14, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/665,892 filed on Aug. 1, 2017, which is acontinuation of U.S. patent application Ser. No. 15/214,564 filed onJul. 20, 2016, which is a continuation of U.S. patent application Ser.No. 14/811,464 filed on Jul. 28, 2015, which is a continuation of U.S.patent application Ser. No. 14/588,712 filed on Jan. 2, 2015, which is acontinuation of U.S. patent application Ser. No. 13/704,010 filed onDec. 13, 2012, which is a national stage application of InternationalApplication No. PCT/JP2011/002802, which claims priority from JapanesePatent Application No. 2010-137339 filed on Jun. 16, 2010. The contentsof these applications are herein incorporated by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a wireless communication device and awireless communication method, and in particular, to a wirelesscommunication device and a wireless communication method for performinginter-cell cooperative transmission/reception or the like in a pluralityof cells.

BACKGROUND ART

At present, in ITU-R (International TelecommunicationUnion-Radiocommunication sector), an IMT (International MobileTelecommunication)-Advanced system is invited. In 3GPP (3rd GenerationPartnership Project), the standardization of LTE-Advanced (LTE-A) whichimproves system performance is performed while keeping backwardcompatibility with Rel. 8 LTE (Release 8 Long Term Evolution).

In RANI of 3GPP, inter-cell cooperative transmission/reception (CoMP:Coordinated Multi-Point Transmission and Reception) which controlstransmission power between many base stations or a transmission basestation on the basis of variation in instantaneous interference power isstudied for LTE-A. In order to realize CoMP, as an addition referencesignal, a pilot signal (CSI-RS: Channel State Information-ReferenceSignal) for down space information estimation is studied. The CSI-RS isa reference signal which is used for estimating frequency characteristicinformation (Channel State Information) of a spatial propagation path ofa line (see NPL 1). It is assumed that a base station which supportsCoMP transmits a CSI-RS. Here, the base station is a cell or an eNB(enhanced Node-B). The CSI-RS should be transmitted to estimate a lineof each cell for CoMP.

FIG. 14 is a schematic view showing when a terminal (UE: User Equipment,mobile station) is given support of CoMP from a plurality of basestations. In order to receive CoMP in a downlink, a terminal 151 shouldreceive CSI-RSs transmitted from a plurality of base stations (cells)161, 162, and 163, and should accurately estimate space information.

FIG. 15 shows a pattern example (R1-101676) of resource disposition whenup to three cells can be multiplexed on four antenna ports as SimulationAssumption agreed on RANI #60. FIG. 15 shows resources which constituteone subframe and one RB (Resource Block). In FIG. 15, the vertical axisrepresents subcarriers (12 subcarriers) of OFDM (Orthogonal FrequencyDivision Multiplexing) at frequency, and the horizontal axis representsOFDM symbols (14 OFDM symbols of #0 to #13) at time. In FIG. 15, onepiece of resource region is one RE (Resource Element). In the patternexample shown in FIG. 15, CSI-RSs of the antenna ports 0 to 3 of a firstcell are transmitted with first to fourth subcarriers of an OFDM symbol#10. CSI-RSs of other second and third cells are allocated to otherfifth to eighth and ninth to twelfth subcarriers in the same OFDM symbol#10 and transmitted (see NPL 2).

FIGS. 16 to 20 show pattern examples (Patterns 1 to 5) of a plurality ofresource dispositions when up to five cells can be multiplexed on eightantenna ports. The examples shown in FIGS. 16 to 20 are pattern examplesobtained by slightly correcting the pattern example (R1-100498) (see NPL3). As in FIG. 15, FIGS. 16 to 20 show resources which constitute onesubframe and one RB. In FIGS. 16 to 20, the vertical axis representssubcarriers (12 subcarriers) of OFDM at frequency, and the horizontalaxis represents OFDM symbols (14 OFDM symbols of #0 to #13) at time.Five Patterns 1 to 5 can correspond to five cells.

In Pattern 1 shown in FIG. 16, CSI-RSs of the antenna ports 0 to 3 ofthe first cell are transmitted with the first, second, seventh, andeighth subcarriers of an OFDM symbol #3, and CSI-RSs of the antennaports 4 to 7 are transmitted with the first, second, seventh, and eighthsubcarriers of an OFDM symbol #10. In Pattern 2 shown in FIG. 17,CSI-RSs of the antenna ports 0 to 3 of the second cell are transmittedwith the third, fourth, ninth, and tenth subcarriers of an OFDM symbol#3, and CSI-RSs of the antenna ports 4 to 7 are transmitted with thethird, fourth, ninth, and tenth subcarriers of an OFDM symbol #10. InPattern 3 shown in FIG. 18, CSI-RSs of the antenna ports 0 to 3 of thethird cell are transmitted with the fifth, sixth, eleventh, and twelfthsubcarriers of an OFDM symbol #3, and CSI-RSs of the antenna ports 4 to7 are transmitted with the fifth, sixth, eleventh, and twelfthsubcarriers of an OFDM symbol #10. In Pattern 4 shown in FIG. 19,CSI-RSs of the antenna ports 0 to 3 of the fourth cell are transmittedwith the third, fourth, ninth, and tenth subcarriers of an OFDM symbol#5, and CSI-RSs of the antenna ports 4 to 7 are transmitted with thethird, fourth, ninth, and tenth subcarriers of an OFDM symbol #12. InPattern 5 shown in FIG. 20, CSI-RSs of the antenna ports 0 to 3 of thefifth cell are transmitted with the third, fourth, ninth, and tenthsubcarriers of an OFDM symbol #6, and CSI-RSs of the antenna ports 4 to7 are transmitted with the third, fourth, ninth, and tenth subcarriersof an OFDM symbol #13.

In FIGS. 15 to 20, in regard to each resource region divided in an REunit, a block A (oblique line) is a region where a CRS (Cell-specificReference Signal) is likely to be transmitted, a block B (dense dot) isa region where a DMRS (DeModulation Reference Signal) is likely to betransmitted, a block C (sparse dot) is a region where a CSI-RS cannot bedisposed, and a block D (empty) is a region where a CSI-RS can bedisposed. In the block C, the leading three OFDM symbols #0 to #2 areregions where a PDCCH (Physical Downlink Control CHannel) is likely tobe transmitted.

As described above, in order that the terminal receives CoMP through adownlink, since it is necessary to receive a CSI-RS transmitted fromeach base station as an additional reference signal and to accuratelyestimate space information, the antenna ports of the base stationsshould orthogonally transmit the CSI-RSs. When multiplexing CSI-RSswhile keeping orthogonality, a maximum of five cells of one subframe isconsidered.

CITATION LIST Non-Patent Literature

[NPL 1] 3GPP TR 36.814 V9.0.0 (2010-03), “3rd Generation PartnershipProject; Technical Specification Group Radio Access Network; EvolvedUniversal Terrestrial Radio Access (E-UTRA); Further advancements forE-UTRA physical layer aspects (Release 9)”

[NPL 2] R1-101676, Huawei, NTT DoCoMo, Nokia, Nokia Siemens Networks,ZTE, Panasonic, Texas Instruments, “CSI-RS simulation assumptions”, 3GPPTSG RAN WG1 Meeting #60, Feb. 22-26, 2010

[NPL 3] R1-100498, NTT DoCoMo, “CSI-RS Inter-cell Design Aspects”, 3GPPTSG RAN WG1 Meeting #59bis, Jan. 18-22, 2010

[NPL 4] 3GPP TS 36.300 V9.3.0 (2010-03), “3rd Generation PartnershipProject; Technical Specification Group Radio Access Network; EvolvedUniversal Terrestrial Radio Access (E-UTRA) and Evolved UniversalTerrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2(Release 9)”

[NPL 5] R1-100144, Samsung, “Considerations on Extended Cell DTX”, 3GPPTSG RAN WG1 Meeting #59bis, Jan. 18-22, 2010

SUMMARY OF INVENTION Technical Problem

In the standardization of LTE-A, for the purpose of power saving of thebase station, extended discontinuous transmission (Extended Cell DTX) isstudied. In order to extend the period of transmission OFF while keepingbackward compatibility with Re1.8 LTE, Extended Cell DTX using FakeMBSFN subframes under the pretense of MBSFN (Multimedia Broadcastmulticast service Single Frequency Network) subframes is studied.

The MBSFN subframes will be described. The MBSFN subframes are subframesfor transmitting data for MBMS (Multimedia Broadcast Multicast Service)as a broadcast/multicast service. In the broadcast/multicast service, itis assumed that the same data is transmitted from a plurality of basestations, the characteristic of OFDM which is used as a transmissionsystem in the downlink of LTE or LTE-A is utilized, and a singlefrequency network mode in which a plurality of cells performtransmission using the same frequency is used (see NPL 4).

Usually, although a base station transmits a CRS in each subframe, andeach terminal receives the CRS and measures the quality of the downlinkor the like, in the MBSFN subframes, a terminal which does not receive aMBSFN subframe receives only a CRS in a head subframe, and does notreceive remaining CRSs in the subframe. For this reason, even when thebase station does not actually transmit a service using MBSFN in acertain subframe, if the terminal is notified that a subframe is a MBSFNsubframe, since the terminal receives only the head CRS, it shouldsuffice that the base station transmit only the head CRS. Reduction intransmission power using this is network energy saving using Fake MBSFNsubframes.

FIG. 21 shows an image example of resource disposition in time series ofsubframes when Extended Cell DTX using Fake MBSFN subframes is applied.The example shown in FIG. 21 shows subframes (subframes #0 to #9) of afirst frame and a second frame with reference to R1-100144 (see NPL 5).In FIG. 21, the horizontal direction represents the elapse of time, anda broken line in the upper portion of each subframe image representsON/OFF of an amplifier (PA: Power Amplifier). In regard to each OFDMsymbol of one subframe, a block A (left downward oblique line) is asymbol which is likely to transmit a CRS, a block B (dense dot) is asymbol which is likely to transmit a PSS (Primary Synchronization Code),a block C (sparse dot) is a symbol which is likely to transmit an SSS(Secondary Synchronization Code), a block D (lattice) is a symbol whichis likely to transmit a BCH (Broadcast CHannel), and a block E (rightdownward oblique line) is a symbol which is likely to transmit an SIB(System Information Block).

Taking into consideration rising or falling of PA, power is requiredwhen there is a transmission symbol and also before and after this time.Accordingly, as in the subframes #4 and #9, when the number oftransmission symbols is at least temporally dispersed, a power savingeffect is lowered. When only the head symbol is transmitted with theapplication of Fake MBSFN to the subframes #1, #2, #3, #6, #7, and #8surrounded by a one-dot-chain line frame, the power saving effect ishigh. When a CSI-RS is transmitted from a base station as an additionalreference signal so as to realize CoMP in the downlink, in FIG. 21, aCSI-RS should be disposed in an empty symbol excluding a symbol which islikely to transmit a CRS or the like, and transmitted. However, if aCSI-RS is transmitted with a subframe to which Fake MBSFN is applied,there is a problem in that the power saving effect is lowered.

The invention has been accomplished in consideration of theabove-described situation, and an object of the invention is to enablethe transmission of a reference signal, such as a CSI-RS, whilemaintaining a power saving effect.

Solution to Problem

According to one aspect of the present invention, there is provided awireless communication device including:

a reference signal generation unit configured to generate a referencesignal to be used for estimating a state of a spatial propagation pathof a communication line;

a disposition unit configured to, when a frame has a plurality ofsubframes separately disposed on at least a time axis, dispose thereference signal in subframes excluding subframes incapable oftransmitting the reference signal from among a plurality of subframesand other than subframes capable of acting as discontinuouscommunication applicable subframes when discontinuous communication isperformed; and

a transmission unit configured to transmit a transmission signalincluding the disposed reference signal.

According to the invention, in the wireless communication device asdescribed above,

the reference signal is a signal which is transmitted from each of aplurality of cells and received for estimating a state of a spatialpropagation path of a communication line from each cell in one terminal.

Therefore, it becomes possible to dispose and transmit the referencesignal used for estimating the state of the spatial propagation path ofthe communication line without causing damage to the power saving effectby discontinuous communication.

According to the invention, in the wireless communication device asdescribed above,

the frame has ten subframes of a subframe #0 to a subframe #9, and

the disposition unit is configured to dispose the reference signalexcluding the subframes #0 and #5 incapable of transmitting thereference signal, and in at least one of the subframes #4 and #9 whichare subframes other than subframes capable of acting as thediscontinuous communication applicable subframes.

Therefore, if the reference signal is transmitted using the subframes #4and #9, it becomes possible to multiplex and transmit the referencesignal while keeping inter-cell orthogonality without causing damage tothe power saving effect by discontinuous communication when transmittingthe reference signal from each of a plurality of cells.

According to the invention, in the wireless communication device asdescribed above,

the disposition unit is configured to dispose the reference signal insubframes including the subframes capable of acting as the discontinuouscommunication applicable subframes when the discontinuous communicationis not performed, and dispose the reference signal in subframes otherthan the subframes capable of acting as the discontinuous communicationapplicable subframes when the discontinuous communication is performed.

Therefore, it becomes possible to secure the number of reference signalswhich can be multiplexed in a plurality of cells.

According to the invention, in the wireless communication device asdescribed above,

the disposition unit is configured to orthogonally dispose the referencesignal such that the reference signal between close cells is multiplexedwith the same subframes and the reference signal between cells otherthan the close cells is multiplexed with different subframes when thediscontinuous communication is not performed, and change and dispose thereference signal from subframes acting as the discontinuouscommunication applicable subframes to subframes other than subframescapable of acting as the discontinuous communication applicablesubframes while maintaining orthogonality within the same subframe whenthe discontinuous communication is performed.

Therefore, it becomes possible to secure the number of reference signalswhich can be multiplexed in a plurality of cells and to keeporthogonality of the reference signal between close cells which arelikely to cause large interference to other cells.

According to the invention, in the wireless communication device asdescribed above,

the frame has 10 subframes of a subframe #0 to a subframe #9, and

the disposition unit is configured to dispose the reference signal in atleast one of the subframes #1, #2, #3, #4, #6, #7, #8, and #9 excludingthe subframes #0 and #5 incapable of transmitting the reference signalwhen the discontinuous communication is not performed, and dispose thereference signal in at least one of the subframes #4 and #9 which aresubframes other than subframes capable of acting as the discontinuouscommunication applicable subframes in regard to subframes acting as thediscontinuous communication applicable subframes when the discontinuouscommunication is performed.

Therefore, it becomes possible to secure the number of reference signalsin a plurality of cells and to keep orthogonality of the referencesignal between close cells which are likely to cause large interferenceto other cells, in particular, to the nearest cells.

According to the invention, in the wireless communication device asdescribed above,

when disposing the reference signal in subframes other than subframesacting as the discontinuous communication applicable subframe when thediscontinuous communication is performed, the disposition unit isconfigured to dispose the reference signal in subframes other thansubframes capable of acting as the discontinuous communicationapplicable subframe in a different frame.

Therefore, if a subframe in which the reference signal is disposed isexpanded to different frames, for example, even when the number ofreference signals which are transmitted between a plurality of cells islarge, it becomes possible to secure temporal orthogonality and tomultiplex a necessary number of reference signals.

According to the invention, the wireless communication device asdescribed above, further including:

a control unit configured to, when the disposition unit disposes thereference signal in subframes other than subframes acting as thediscontinuous communication applicable subframes when the discontinuouscommunication is performed, notify an another communication apparatus ofsubframe numbers acting as the discontinuous communication applicablesubframes.

Therefore, if only the subframe number which acts as a discontinuouscommunication applicable subframe is notified, even when detailedmapping information is not sent to an anther communication apparatus, itbecomes possible to mutually recognize the subframes in which thereference signal is disposed. For this reason, even when complicatedmapping information is not sent, it is possible to receive and extractthe reference signal on the reception side even after discontinuouscommunication is performed.

According to another aspect of the present invention, there is provideda wireless communication device including:

a reception unit configured to receive a signal including a referencesignal to be used for estimating a state of a spatial propagation pathof a communication line;

a separation unit configured to, when a frame has a plurality of framesseparately disposed on at least a time axis, separate the referencesignal disposed in subframes excluding subframes incapable oftransmitting the reference signal and other than subframes capable ofacting as discontinuous communication applicable subframes whendiscontinuous communication is performed from among the plurality ofsubframes from the received signal on the basis of dispositioninformation of the reference signal; and

a space estimation unit configured to estimate the state of the spatialpropagation path on the basis of the separated reference signal.

Therefore, it becomes possible to perform space information estimationof the communication line on the basis of the received reference signalto generate space information which is reported to the wirelesscommunication device on the transmission side. At this time, when thereference signals which are transmitted from a plurality of cells in acellular system and multiplexed between cells are received, it ispossible to generate space information which is reported to a wirelesscommunication device of a currently communicating cell and a wirelesscommunication device of an adjacent cell.

According to the invention, in the wireless communication device asdescribed above,

the reference signal is a CSI-RS (Channel State Information-ReferenceSignal) which is used for estimating frequency characteristicinformation (Channel State Information) of the spatial propagation pathof the communication line.

According to the invention, in the wireless communication device asdescribed above,

the discontinuous communication applicable subframes are MBSFN(Multimedia Broadcast multicast service Single Frequency Network)subframes which are used for discontinuous communication by ExtendedCell DTX (Discontinuous Transmission).

Therefore, when achieving power saving through Extended Cell DTX whichis studied in LTE-A, it becomes possible to dispose and transmit aCSI-RS without causing damage to the power saving effect bydiscontinuous communication.

According to another aspect of the present invention, there is provideda wireless communication method including:

generating a reference signal to be used for estimating a state of aspatial propagation path of a communication line;

when a frame has a plurality of subframes separately disposed on atleast a time axis, disposing the reference signal in subframes excludingsubframes incapable of transmitting the reference signal and other thansubframes capable of acting as discontinuous communication applicablesubframes when discontinuous communication is performed from among theplurality of subframes; and

transmitting a transmission signal including the disposed referencesignal.

According to another aspect of the present invention, there is provideda method of estimating a propagation path, the method including:

receiving a signal including a reference signal to be used forestimating a state of a spatial propagation path of a communicationline;

when a frame has a plurality of frames separately disposed on at least atime axis, separating the reference signal disposed in subframesexcluding subframes incapable of transmitting the reference signal andother than subframes capable of acting as discontinuous communicationapplicable subframes when discontinuous communication is performed fromamong the plurality of subframes from the received signal on the basisof disposition information of the reference signal; and

estimating the state of the spatial propagation path on the basis of theseparated reference signal.

Advantageous Effects of Invention

According to the invention, it is possible to enable the transmission ofthe reference signal, such as a CSI-RS, while maintaining the powersaving effect.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing the schematic configuration of a frame and asubframe of a transmission signal in a wireless communication system ofthis embodiment.

FIG. 2 is a diagram showing a first disposition example of a CSI-RS of asubframe in a first embodiment.

FIG. 3 is a diagram showing a second disposition example of a CSI-RS ofa subframe in the first embodiment.

FIG. 4 is a block diagram showing the configuration of a base station inthe first embodiment.

FIG. 5 is a block diagram showing the configuration of a terminal in thefirst embodiment.

FIG. 6 is a diagram showing a disposition example of a subframe whichtransmits a CSI-RS of a frame at a normal time in a second embodiment.

FIG. 7 is a diagram showing a disposition example of a subframe whichtransmits a CSI-RS of a frame during the execution of Extended Cell DTXin the second embodiment.

FIG. 8 is a block diagram showing the configuration of a base station inthe second embodiment.

FIG. 9 is a block diagram showing the configuration of a terminal in thesecond embodiment.

FIG. 10 is a diagram showing the transition of the disposition of aCSI-RS to each subframe when changing from the normal time to theexecution of Extended Cell DTX.

FIG. 11 is a diagram showing a disposition example of a subframe whichtransmits a CSI-RS in a plurality of subframes during the execution ofExtended Cell DTX in a third embodiment.

FIG. 12 is a block diagram showing the configuration of a base stationin the third embodiment.

FIG. 13 is a block diagram showing the configuration of a terminal inthe third embodiment.

FIG. 14 is a schematic view when a terminal which is given support ofCoMP from a plurality of base stations.

FIG. 15 is a diagram showing a pattern example of resource dispositionwhen up to three cells can be multiplexed on four antenna ports.

FIG. 16 is a diagram showing a pattern example (Pattern 1) of resourcedisposition when up to five cells can be multiplexed on eight antennaports.

FIG. 17 is a diagram showing a pattern example (Pattern 2) of resourcedisposition when up to five cells can be multiplexed on eight antennaports.

FIG. 18 is a diagram showing a pattern example (Pattern 3) of resourcedisposition when up to five cells can be multiplexed on eight antennaports.

FIG. 19 is a diagram showing a pattern example (Pattern 4) of resourcedisposition when up to five cells can be multiplexed on eight antennaports.

FIG. 20 is a diagram showing a pattern example (Pattern 5) of resourcedisposition when up to five cells can be multiplexed on eight antennaports.

FIG. 21 is a diagram showing an image example of resource disposition intime series of each subframe when Extended Cell DTX using Fake MBSFNsubframes is applied.

DESCRIPTION OF EMBODIMENTS

In this embodiment, as a wireless communication system to which awireless communication device and a wireless communication methodaccording to the invention are applied, a configuration example in acellular system for mobile communication, such as a mobile phone, isshown. A case where a CSI-RS which is studied in LTE-A is transmitted asan additional reference signal which is used along with a referencesignal used heretofore is illustrated. A CSI-RS is a reference signalwhich is transmitted in a plurality of cells along with a referencesignal, such as a CRS, transmitted in each cell so as to realize CoMP,and is used for estimating the state (CSI in LTE-A) of a spatialpropagation path of a communication line. In this embodiment, it isassumed that, in a wireless communication system, discontinuouscommunication is performed to achieve power saving. A case whereExtended Cell DTX which is studied in LTE-A is performed asdiscontinuous communication is illustrated. In Extended Cell DTX, anMBSFN subframe is used as a discontinuous communication applicablesubframe when discontinuous communication is performed.

First Embodiment

A first embodiment is a first example of the disposition of a CSI-RSacting as an additional reference signal, and when Extended Cell DTX(discontinuous communication) is performed, a CSI-RS is transmitted withsubframes other than subframes capable of acting as MBSFN subframes(discontinuous communication applicable subframes).

FIG. 1 is a diagram showing the schematic configuration of a frame and asubframe of a transmission signal in a wireless communication system ofthis embodiment. The example of FIG. 1 shows the frame configuration ofa transmission signal in a downward direction from a base station (cell)to a terminal in a cellular system, and the horizontal axis representstime.

As shown in the upper portion of FIG. 1, one frame has ten subframes.One subframe is, for example, 1 ms, and one frame is, for example, 10ms. The subframes of the frame are identified with subframe numbers(subframes #0 to #9). In the discussion of 3GPP, as shown in FIG. 21, aCSI-RS is not transmitted with the subframes #0 and #5, and in FIG. 1,the lower left side represents a subframe of a block indicated by a leftdownward oblique line. When Extended Cell DTX is performed, in order toperform power saving using Fake MBSFN subframes, subframes which can actas the MBSFN subframes are used. At this time, the subframes #4 and #9do not act as MBSFN subframes, and in FIG. 1, represent subframes of ahorizontally striped block. Other subframes are subframes which can actas MBSFN subframes, and in FIG. 1, represent subframes of a sparselydotted block. In the subframes which can act as MBSFN subframes, if theeffect that MBSFN is used is notified, it should suffice that only thehead CRS is transmitted. In this embodiment, a CSI-RS is disposed insubframes other than subframes capable of acting as MBSFN subframes,that is, the subframes #4 and #9 which cannot act as MBSFN subframes andcan transmit a CSI-RS. In this case, a CSI-RS of a certain cell istransmitted, for example, in each frame, that is, at an interval of 10ms. The transmission interval of a CSI-RS may be increased to 20 msinterval, 40 ms interval, or the like.

The lower side of FIG. 1 shows the configuration of the subframes #4 and#9, and is an image of resource disposition in time series of thesesubframes. The subframes #4 and #9 cannot act as MBSFN subframes, andfor this reason, it is not possible to reduce CRS transmission usingFake MBSFN subframes. Accordingly, when four or more antenna ports areprovided, as shown in the lower portion of FIG. 1, CRS transmissionsignals are in at least OFDM symbols #0, #1, #4, #7, #8, and #11(symbols of a block indicated by a left downward oblique line). In thiscase, since the transmission signals are dispersed in the temporaldirection, even if there were no transmission signals other than CRS,the amplifier (PA) is frequently turned ON/OFF, and the power savingeffect is not high. In this way, in the subframes #4 and #9, since thepower saving effect is not expected. For this reason, when transmittinga CSI-RS, signals which should be transmitted are transmitted with thesubframes #4 and #9, and are not disposed in other subframes, therebyincreasing the power saving effect as the entire system.

FIG. 2 is a diagram showing a first disposition example of a CSI-RS of asubframe in the first embodiment. The first disposition example of FIG.2 shows an image of resource disposition of the subframes #4 and #9 whena CSI-RS is transmitted with the OFDM symbol #10. As described above, inthe subframes #4 and #9, CRSs are transmitted with the OFDM symbols #0,#1, #4, #7, #8, and #11 (symbols of a block indicated by a left downwardoblique line). In this case, as shown in FIG. 15, in the OFDM symbol #10(a symbol of a block indicated by a vertical stripe), CSI-RSs of aplurality of antenna ports are orthogonally multiplexed with a frequencydomain, and CSI-RSs which are transmitted from other base stations(cells) are transmitted using other REs (other subcarriers) of the sameOFDM symbol #10.

FIG. 3 is a diagram showing a second disposition example of a CSI-RS ofa subframe in the first embodiment. The second disposition example ofFIG. 3 shows an image of resource disposition of the subframes #4 and #9when CSI-RSs are transmitted with the OFDM symbols {#3,#10}, {#5,#12},{#6,#13}. In this case, as shown in FIGS. 16 to 20, in the OFDM symbols{#3,#10}, {#5,#12}, {#6,#13}, frequency domain multiplexing in the sameOFDM symbol or time domain multiplexing by a different OFDM symbol isused to orthogonally multiplex CSI-RSs which are transmitted from aplurality of antenna ports or base stations (cells).

In this way, in the first embodiment, when a CSI-RS as an additionalreference signal is transmitted so as to perform CoMP or the like, theCSI-RS is transmitted using subframes other than subframes capable ofacting as MBSFN subframes when performing Extended Cell DTX using FakeMBSFN subframes, specifically, the subframes #4 and #9. Accordingly,when Extended Cell DTX is performed to achieve power saving, a CSI-RScan be transmitted while maintaining the power saving effect. Therefore,it is possible to achieve the power saving effect when a CSI-RS istransmitted from a base station to a terminal.

Hereinafter, as an example of the configuration of the wirelesscommunication device in this embodiment, the configuration of a basestation and a terminal (mobile station) will be described.

<Configuration and Operation of Base Station>

FIG. 4 is a block diagram showing the configuration of a base station100 in the first embodiment. The base station (base station device) 100includes a setting unit 101, a control unit 102, a CRS generation unit104, a CSI-RS generation unit 105, a modulation unit 106, a dispositionunit 107, an IFFT (Inverse Fast Fourier Transform) unit 108, a CP(Cyclic Prefix) addition unit 109, a distribution unit 112, a plurality(in this case, M) of transmission RF (Radio Frequency) units 110-1 to110-M, and a plurality (in this case, M) of antennas 111-1 to 111-M.

The setting unit 101 sets (configures) the generation of a CRS, and whenit is necessary to transmit a CSI-RS so as to support CoMP, and sets thegeneration of a CSI-RS. The setting unit 101 outputs these kinds ofsetting information to the control unit 102, the CRS generation unit104, and the CSI-RS generation unit 105.

The control unit 102 controls resource disposition in the dispositionunit 107 and the distribution of transmission signals in thedistribution unit 112 on the basis of the setting information input fromthe setting unit 101. In order to notify a terminal in a host cell or anear cell of setting information including CSI-RS dispositioninformation, the control unit 102 outputs the setting information to thedisposition unit 107 to transmit the setting information as a controlsignal of an upper-level layer.

The CRS generation unit 104 generates a CRS on the basis of the settinginformation input from the setting unit 101. The CRS generation unit 104outputs the generated CRS to the disposition unit 107.

The CSI-RS generation unit 105 realizes the function of a referencesignal generation unit, and generates a CSI-RS on the basis of thesetting information input from the setting unit 101. The CSI-RSgeneration unit 105 outputs the generated CSI-RS to the disposition unit107.

The modulation unit 106 channel-encodes and modulates input transmissiondata (downlink data), and output a data signal after modulation to thedisposition unit 107.

The disposition unit 107 multiplexes the CRS input from the CRSgeneration unit 104, the CSI-RS input from the CSI-RS generation unit105, and the data signal (that is, PDSCH: Physical Downlink SharedCHannel) input from the modulation unit 106. When there is a controlsignal of an upper-level layer for giving notification of the settinginformation from the control unit 102, the disposition unit 107 disposesinformation of the control signal in the data signal (PDSCH). Here,disposition unit 107 disposes (multiplexes) the CRS, the CSI-RS, and thedata signal (PDSCH) in the respective resource blocks of the downlink.At this time, the disposition unit 107 multiplexes the CSI-RS such thatthe CSI-RS is disposed in the subframe #4 or #9. In regard to thedisposition of the CSI-RS or the like in the disposition unit 107, forexample, the disposition example shown in FIG. 2 or 3 is considered. Thedisposition unit 107 outputs the multiplexed signal to the IFFT unit108.

The IFFT unit 108 performs IFFT processing on the signal input from thedisposition unit 107, and acquires a time domain signal. The IFFT unit108 outputs the time domain signal to the CP addition unit 109.

The CP addition unit 109 adds a CP to the time domain signal input fromthe IFFT unit 108, and outputs the signal after CP addition to thedistribution unit 112. The distribution unit 112 outputs thecorresponding signals to the transmission RF units 110-1 to 110-M underthe control of the control unit 102. The signals for all of Mtransmission antennas are input to the distribution unit 112, and arecorrespondingly distributed to the antennas.

The transmission RF units 110-1 to 110-M perform transmissionprocessing, such as D/A (Digital to Analog) conversion, up-convert, andamplification, on the signals input from the distribution unit 112, andtransmit and output the signals subjected to the transmission processingfrom the antennas 111-1 to 111-M as transmission radio signals (in thiscase, OFDM signals). The transmission radio signals are transmitted tothe terminal in a wireless manner. Here, the transmission RF units 110-1to 110-M and the antennas 111-1 to 111-M realize the function of atransmission unit.

<Configuration and Operation of Terminal (Mobile Station)>

FIG. 5 is a block diagram showing the configuration of a terminal 200 inthe first embodiment. The terminal (mobile station device) 200 includesa plurality (in this case, N) of antennas 201-1 to 201-N, a plurality(in this case, N) of reception RFs units 202-1 to 202-N, an aggregationunit 218, a CP elimination unit 203, an FFT (Fast Fourier Transform)unit 204, a separation unit 205, a CRS reception line estimation unit206, a CSI-RS reception space information estimation unit 207, a PDSCHreception unit 208, a line quality information generation unit 215, aspace information generation unit 216, a setting information receptionunit 217, a modulation unit 209, a DFT (Discrete Fourier Transform) unit210, a disposition unit 211, an IFFT unit 212, a CP addition unit 213, adistribution unit 219, and a plurality (in this case, N) of transmissionRF units 214-1 to 214-N. Here, an antenna, a transmission RF unit, and areception RF unit are collectively called an RF block. As in theillustrated example, when the number of antennas is N, the terminal 200has N RF blocks 220-1 to 220-N. These RF blocks 220-1 to 220-N realizethe function of a reception unit.

The reception RF units 202-1 to 202-N are configured such that thereception band is changeable, and changes the reception band inaccordance with a reception signal. The reception RF units 202-1 to202-N perform reception radio processing (down-convert, A/D (Analog toDigital) conversion, and the like) on the reception radio signals (inthis case, OFDM signals) received through the antennas 201-1 to 201-N,and output the obtained reception signals to the aggregation unit 218.The aggregation unit 218 aggregates the reception signals input from theRF blocks 202-1 to 202-N, and outputs the reception signals to the CPelimination unit 203.

The CP elimination unit 203 eliminates the CP from the reception signalsinput from the reception RF units 202-1 to 202-N of the RF blocks 202-1to 202-N, and outputs the signals after CP elimination to the FFT unit204.

The FFT unit 204 performs FFT processing on each signal input from theCP elimination unit 203 to acquire a frequency domain signal. The FFTunit 204 outputs the frequency domain signal to the separation unit 205.

The separation unit 205 separates the frequency domain signal input fromthe FFT unit 204 into the CRS, the CSI-RS, and the data signal (that is,PDSCH). The separation unit 205 outputs the CRS to the CRS receptionline estimation unit 206, outputs the CSI-RS to the CSI-RS receptionspace information estimation unit 207, and outputs the PDSCH to thePDSCH reception unit 208 on the basis of setting information receivedwith previous subframes. The separation unit 205 acquires the controlsignal of the upper-level layer including the setting information, andoutputs the control signal to the setting information reception unit217.

The setting information reception unit 217 reads the setting informationincluding the CSI-RS disposition information from the control signalinput from the separation unit 205, and outputs the setting informationto the separation unit 205. The separation unit 205 separates andextracts a CSI-RS disposed in a predetermined subframe on the basis ofthe CSI-RS disposition information in the setting information. Thesetting information reception unit 217 outputs the setting information,such as a back-diffusion code for receiving and demodulating a CSI-RS,to the CSI-RS reception space information estimation unit 207.

The CRS reception line estimation unit 206 estimates the downlinktransmitted from the base state to the mobile station device itself bythe CRS input from the separation unit 205, and outputs the lineestimation value of the downlink to the line quality informationgeneration unit 215. The line quality information generation unit 215generates line quality information to be reported to the base station onthe basis of the line estimation value input from the CRS reception lineestimation unit 206. The line quality information to be generated is,for example, a CQI (Channel Quality Indicator) or the like.

The CSI-RS reception space information estimation unit 207 realizes thefunction of a space estimation unit, and performs space informationestimation of the downlink transmitted from the base station to themobile station device itself by the CSI-RS input from the separationunit 205 using the setting information of the CSI-RS input from thesetting information reception unit 217. The CSI-RS reception spaceinformation estimation unit 207 inputs the space estimation informationof the downlink to the space information generation unit 216. The spaceinformation generation unit 216 generates space information to bereported to the base station on the basis of the space estimationinformation input from the CSI-RS reception space information estimationunit 207. The space information estimation is performed on anotherperipheral base station as a subject for CoMP as well as a base stationwith which the mobile station device itself performs communication.

The PDSCH reception unit 208 demodulates and channel-decodes the PDSCHinput from the separation unit 205, and acquires reception data.

The modulation unit 209 channel-encodes and modulates input transmissiondata (uplink data), and outputs the data signal after modulation to theDFT unit 210.

The DFT unit 210 performs DFT processing on the data signal input fromthe modulation unit 209 to acquire a frequency domain signal. The DFTunit 210 outputs the frequency domain signal to the disposition unit211.

The disposition unit 211 disposes the line quality information inputfrom the line quality information generation unit 215, the spaceinformation input from the space information generation unit 216, andthe frequency domain signal input from the DFT unit 210 in the resourceblocks of the uplink.

The IFFT unit 212 performs IFFT processing on the frequency domainsignal input from the disposition unit 211, and acquires a time domainsignal. The IFFT unit 212 outputs the time domain signal to the CPaddition unit 213.

The CP addition unit 213 adds a CP to the time domain signal input fromthe IFFT unit 212, and outputs the signal after CP addition to thedistribution unit 219. The distribution unit 219 outputs thecorresponding signals to the transmission RF units 214-1 to 214-N of theRF blocks 220-1 to 220-N. The signals for all of N transmission antennasare input to the distribution unit 219, and are correspondinglydistributed to the antennas.

The transmission RF units 214-1 to 214-N perform transmissionprocessing, such as D/A (Digital to Analog) conversion, up-convert, andamplification, on the signals input from the distribution unit 219, andtransmit and output the signals subjected to the transmission processingfrom the antennas 201-1 to 201-N as transmission radio signals. Thetransmission radio signals are transmitted to the base station in awireless manner.

According to the first embodiment, in the base station, if a CSI-RS istransmitted with subframes other than subframes capable of acting asMBSFN subframes when Extended Cell DTX is performed, it is possible totransmit a CSI-RS without causing damage to the power saving effectusing Fake MBSFN subframes. At this time, only if the effect that MBSFNis used is notified from the base station to the terminal, the terminalwhich can address MBSFN can identify MBSFN subframes and othersubframes, and can appropriately receive a CSI-RS. In the terminal,space information estimation of the downlink is performed on the basisof the received CSI-RS, and space information which is reported to acurrently communicating base station and a peripheral base station as asubject for CoMP can be generated.

Second Embodiment

A second embodiment is a second example of disposition of a CSI-RS as anadditional reference signal. In the second embodiment, in order tosecure the number of multiplexes of a CSI-RS, at the normal time whenExtended Cell DTX is not performed, a CSI-RS is transmitted withsubframes capable of acting as MBSFN subframes, and when Extended CellDTX is performed, a CSI-RS is transmitted with subframes incapable ofacting as MBSFN subframes. At this time, when focusing on thatinterference when orthogonality of the CSI-RS is collapsed becomes smallwith an increasing distance, CSI-RSs of a plurality of cells aremultiplexed in accordance with the distance between the cells takinginto consideration the disposition of the cells.

If the subframes which transmit a CSI-RS are limited to the subframes #4and #9, the number of CSI-RSs which can be multiplexed becomes smallwhile keeping orthogonality between the cells. When Extended Cell DTXusing Fake MBSFN subframes is not performed, CSI-RSs for five cells ineach subframe can be multiplexed, and thus CSI-RSs for 5 cells×8subframes=40 cells can be multiplexed in the subframes other than thesubframes #0 and #5 while keeping orthogonality. However, if only thesubframes #4 and #9 are used, only CSI-RSs for 5 cells×2 subframes=10cells can be multiplexed. A CSI-RS is used for CoMP line estimation(space information estimation), and in order that line estimation isperformed in a terminal of another cell, it is necessary to keeporthogonality between close cells, in particular, between adjacentcells.

In order to respond to the above-described problem, in the secondembodiment, at the normal time, a CSI-RS is orthogonally multiplexedusing a different RE in the same subframes between close cells, and aCSI-RS is multiplexed with different subframes between other separatecells. That is, at the normal time, a CSI-RS is transmitted usingsubframes capable of acting as MBSFN subframes along with the subframes#4 and #9. When Extended Cell DTX is performed, a CSI-RS is changed fromsubframes (subframes #1, #2, #3, #6, #7, and #8) capable of acting asMBSFN subframes to other subframes (subframe #4 or #9) and mapped whilekeeping orthogonality in the subframes. In regard to the change of thedisposition of a CSI-RS from subframes capable of acting as MBSFNsubframes to other subframes, the disposition of a CSI-RS of eachsubframe and the change timing may be appropriately set in accordancewith the disposition of the cells.

FIG. 6 is a diagram showing a disposition example of subframes whichtransmit a CSI-RS in a frame at a normal time in the second embodiment.At the normal time, that is, when Extended Cell DTX to which Fake MBSFNsubframes are applied is not performed, it is assumed that CSI-RSsbetween close cells, in particular, between the closes (adjacent) cellsare orthogonally multiplexed with the same subframes, and CSI-RSsbetween other cells are multiplexed with different subframes. In theillustrated example, CSI-RSs between the nearest cells are multiplexedin the same subframes, such as the subframe #1, and CSI-RSs betweenother separate cells are multiplexed in other subframes, such as thesubframes #1, #2, #3, and #4. Here, cells in which multiplexing isperformed in the same subframes are called a CSI-RS group. Basically, ifCSI-RSs between the nearest cells are multiplexed with the samesubframes, while there are not other restrictions, CSI-RSs may bemultiplexed with subframes separated in time with an increasing distancebetween the cells.

FIG. 7 is a diagram showing a disposition example of subframes whichtransmit a CSI-RS in a frame during the execution of Extended Cell DTXin the second embodiment. When Fake MBSFN subframes are applied and anExtended Cell DTX mode is executed, CSI-RSs which are transmitted withsubframes acting as Fake MBSFN subframe are changed to subframesincapable of acting as MBSFN subframes, that is, the subframe #4 or #9and mapped while keeping orthogonality between the CSI-RSs in thesubframes (while keeping relative CSI-RS multiplex-disposition in thesubframes). That is, the subframe to which the CSI-RS group is allocatedis changed to the subframe #4 or #9 while keeping orthogonality in theCSI-RS group.

When mapping to the subframe #4 or #9, if orthogonality between CSI-RSsin the subframes is kept, other restrictions are not required; however,the simplest case is a method in which mapping is made while keeping aresource disposition pattern in the same subframe. While there is noproblem if mapping is made in either the subframe #4 or #9, it is easyto map the subframes (subframes #1 to #3) of the first half of the frameto the subframe #4, and to map the subframes (subframes #6 to #8) of thesecond half of the frame to the subframe #9. In this case, the basestation notifies only the subframe number which is changed to the MBSFNsubframe, and the terminal which receives a CSI-RS with this subframecan receive the CSI-RS simply with the same RE of the subframe #4 if theCSI-RS is originally received with the first half of the frame, and canreceive the CSI-RS simply with the same RE of the subframe #9 if theCSI-RS is originally received with the second half of the frame.

The subframe number which is changed to the MBSFN subframe is notifiedwith MBSFN-SubframeConfig included in SIB2 (System Information BlockType2) of RRC (Radio Resource Control) information elements as thecontrol signal of the upper-level layer. In MBSFN-SubframeConfig, asubframe which acts as an MBSFN subframe is notified assubframeAllocation (see reference NPL 1 described below).

In subframeAllocation, there are oneFrame for one frame and fourFramesfor four frames, and either one is used. In the case of oneFrame,whether six subframes which can be applied to MBSFN subframes in oneframe are set as MBSFN subframes or normal non-MBSFN subframes isnotified in one subframe unit. In the case of fourFrames, for 24subframes which can be applied to MBSFN subframes in four subframes,notification is given in one subframe unit. AsradioframeAllocationPeriod, a frame interval at which an MBSFN subframeis transmitted is set. The radioframeAllocationPeriod includes n1, n2,n4, n8, n16, and n32. For example, if n1 is used, theradioframeAllocationPeriod becomes a one-frame interval, and if n2 isused, the radioframeAllocationPeriod becomes a two-frame interval.However, the use of n1 and n2 of the radioframeAllocationPeriod islimited to when subframeAllocation is oneFrame, n4 or more is used forfourFrames.

Accordingly, for example, when the subframe #1 is changed to theExtended Cell DTX mode to which Fake MBSFN subframes are applied, afteroneFrame is used with subframeAllocation of MBSFN-SubframeConfig, thesubframe #1 is set as an MBSFN subframe, and theradioframeAllocationPeriod is set to n1.

[Reference NPL 1] 3GPP TS 36.331 V9.2.0 (2010-03), “3rd GenerationPartnership Project; Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Radio ResourceControl (RRC); Protocol specification (Release 9)”

<Configuration and Operation of Base Station>

FIG. 8 is a block diagram showing the configuration of a base station300 in the second embodiment. The base station 300 is different from thebase station 100 of the first embodiment shown in FIG. 4 in that theoperations of a setting unit 301, a control unit 302, a CSI-RSgeneration unit 305, and a disposition unit 307 are different. Otherparts are the same as those in the first embodiment, and descriptionthereof will not be repeated.

The operation of the characteristic base station 300 in the secondembodiment will be described. The setting unit 301 outputs settinginformation including CSI-RS disposition information at the normal time(normal mode) and during the execution of Extended Cell DTX (ExtendedCell DTX mode). The control unit 302 performs operation control relatingto CSI-RS transmission in each mode on the basis of the settinginformation from the setting unit 301. When changing from the normalmode to the Extended Cell DTX mode, the control unit 302 outputs controlinformation for reporting subframe numbers acting as MBSFN subframes tothe disposition unit 307, transmits only a subframe number to be changedto an MBSFN subframe as the control signal of the upper-level layer, andgives notification to the terminal.

The CSI-RS generation unit 305 generates a CSI-RS at the normal time andduring the execution of Extended Cell DTX on the basis of the settinginformation input from the setting unit 301. At the normal time, thedisposition unit 307 orthogonally multiplexes CSI-RSs between thenearest cells in the same subframes from the subframes #1, #2, #3, #4,#6, #7, #8, and #9, and multiplexes CSI-RSs between other separate cellswith different subframes. During the execution of Extended Cell DTX, fora subframe which is changed to an MBSFN subframe, the disposition unit307 changes a CSI-RS from among CSI-RSs multiplexed in the subframes #1,#2, #3, #6, #7, and #8 to the subframe #4 or #9 and multiplexes theCSI-RS while keeping relative CSI-RS multiplex-disposition in thesubframe.

<Configuration and Operation of Terminal (Mobile Station)>

FIG. 9 is a block diagram showing the configuration of a terminal 400 inthe second embodiment. The terminal 400 is different from the terminal200 of the first embodiment shown in FIG. 5 in that the operations of aseparation unit 405, a CSI-RS reception space information estimationunit 407, and a setting information reception unit 417 are different.Other parts are the same as those in the first embodiment, anddescription will not be repeated.

The operation of the characteristic terminal 400 in the secondembodiment will be described. The separation unit 405 acquires thecontrol signal of the upper-level layer including the settinginformation from the signal input from the FFT unit 204, and outputs thecontrol signal to the setting information reception unit 417. Thesetting information reception unit 417 reads the setting informationincluding the CSI-RS disposition information from the control signalinput from the separation unit 405, and outputs the setting informationto the separation unit 405. The setting information reception unit 417outputs the setting information, such as a back-diffusion code forreceiving and demodulating a CSI-RS, to the CSI-RS reception spaceinformation estimation unit 407.

The separation unit 405 separates the frequency domain signal input fromthe FFT unit 204 on the basis of the setting information received withthe previous subframes, acquires the CSI-RS, and outputs the CSI-RS tothe CSI-RS reception space information estimation unit 407. At thistime, at the normal time and during the execution of Extended Cell DTX,the separation unit 405 acquires the CSI-RS in accordance with mappingof the CSI-RS to each subframe by the base station, and outputs theCSI-RS to the CSI-RS reception space information estimation unit 407.

At the normal time and during the execution of the Extended Cell DTX,the CSI-RS reception space information estimation unit 407 performsspace information estimation of the downlink transmitted from the basestation to the mobile station device itself by the CSI-RS input from theseparation unit 405 using the setting information of the CSI-RS inputfrom the setting information reception unit 417.

FIG. 10 is a diagram showing a transition example of the disposition ofa CSI-RS to each subframe when changing from the normal time to theexecution of Extended Cell DTX. In FIG. 10, in a situation in which aframe transmitting a CSI-RS in the normal mode is gradually changed tothe Extended Cell DTX mode using Fake MBSFN subframes, thecorrespondence of the subframe at that time and the cell disposition isshown collectively. In the drawing, it is assumed that one macro cell171 indicated by a hexagon has a plurality of sector cells constitutedby one eNB or about five individual cells of small transmission powercells, such as RRH (Remote Radio Head), and the CSI-RSs of the cells inone macro cell 171 are orthogonally multiplexed in the same subframe.Accordingly, about five CSI-RSs are multiplexed in one subframe. In FIG.10, the number (#1 or the like) described in the macro cell 171represents which subframe in the frame is used when transmitting aCSI-RS.

At the normal time shown on the upper side of FIG. 10, since the CSI-RSsof different macro cells 171 are transmitted with different subframes,the CSI-RSs are orthogonalized. When changing to the Extended Cell DTXmode, it is preferable that, in case of moving a CSI-RS to the subframes#4 and #9, CSI-RSs which are multiplexed in the same subframe do notbecome CSI-RSs between adjacent macro cells 171. For this reason, at thebeginning of the change to the Extended Cell DTX mode shown in themiddle of FIG. 10, the CSI-RSs of the subframes #2 and #3, and #7 and #8are preferentially changed to the subframes #4 and #9. In this case,even if four subframes are put in the Extended Cell DTX mode using FakeMBSFN subframes, CSI-RSs between adjacent macro cells 171 can bemultiplexed with different subframes. In this way, it is possible tosuppress the amount of increase in interference between CSI-RSs to besmall. The total number of multiplexes of the CSI-RS is maintained withno change compared to the normal time.

As shown on the lower side of FIG. 10, when the change to the ExtendedCell DTX mode proceeds, the CSI-RSs of the subframes #1 and #6 arechanged to the subframes #4 and #9 and mapped. In this case,orthogonality of the CSI-RS in each macro cell 171 is kept, and when theExtended Cell DTX mode proceeds to the maximum (the ratio ofdiscontinuous communication increases), since it is assumed that thenumber of terminals is small, it is considered that interference betweenCSI-RSs does not cause a large problem.

According to the second embodiment, if orthogonality of the CSI-RSbetween cells is sacrificed while maintaining orthogonality of theCSI-RS in the same cell, it is possible to secure the number ofmultiplexes of the CSI-RS in a plurality of cells, and to keeporthogonality of the CSI-RS between the nearest cells which cause largeinterference to other cells. At this time, while the CSI-RSs betweencells other than the nearest cells may not keep orthogonality, sincethese cells are cells at a distance, large interference is not caused.In regard to the change of the disposition of the CSI-RS, even whencomplicated mapping information is not sent from the base station to theterminal, the CSI-RS can be received even when changed to the ExtendedCell DTX mode.

Third Embodiment

A third embodiment is a third example of the disposition of a CSI-RS asan additional reference signal. In the third embodiment, in order tosecure the number of multiplexes of a CSI-RS and reduce interference ofa CSI-RS between cells, when changing to the Extended Cell DTX mode, aCSI-RS is disposed over a plurality of frames.

In the third embodiment, as in the second embodiment, at the normal timeat which Extended Cell DTX is not performed, CSI-RSs between the nearestcells are orthogonally multiplexed (using different REs) in the samesubframe other than the subframes #0 and #5, and CSI-RSs between otherseparate cells are multiplexed with different subframes. As a mappingrule of CSI-RSs in case of changing to the Extended Cell DTX mode, amapping rule is defined such that neighboring frames as well as thesubframe #4 or #9 in the same frame are used, and the change to thesubframe #4 or #9 of a plurality of frames is made. That is, in case ofdisposing CSI-RSs in the subframe #4 or #9, the CSI-RSs are dispersed inother frames as well as the same frame.

FIG. 11 is a diagram showing a disposition example of a subframe whichtransmits a CSI-RS in a plurality of frames during the execution ofExtended Cell DTX in the third embodiment. FIG. 11 shows an examplewhere CSI-RSs are mapped over a plurality of frames, for example, overtwo frames. Here, in regard to the first half of the first frame, theCSI-RSs of the subframes #1 and #3 are changed and aggregated to thesubframe #4 of the first frame, and the CSI-RSs of the subframes #2 and#4 are changed and aggregated to the subframe #4 of the second frame.Similarly, in regard to the second half of the first frame, the CSI-RSsof the subframes #6 and #8 are changed and aggregated to the subframe #9of the first frame, and the CSI-RSs of the subframes #7 and #9 arechanged and aggregated to the subframe #9 of the second frame. In thiscase, the interval at which a CSI-RS of a certain cell is transmittedincreases; however, when the Extended Cell DTX mode is put, it isassumed that the number of terminals is small. Therefore, it isconsidered that there is no problem even when CSI-RSs are nottransmitted frequently as much.

As in the second embodiment, a subframe number which is changed to anMBSFN subframe may be notified with MBSFN-SubframeConfig included inSIB2 of RRC information elements as the control signal of theupper-level layer. In MBSFN-SubframeConfig, as subframeAllocation, asubframe which acts as an MBSFN subframe is notified. Here, in case ofchanging to the Extended Cell DTX mode, as shown in FIG. 11, whenCSI-RSs are aggregated over two frames, after oneFrame is used withsubframeAllocation of MBSFN-SubframeConfig, the subframes #1, #2, #3,#6, #7, and #8 are set as MBSFN subframes, theradioframeAllocationPeriod is set to n1. In addition, the terminal findsa subframe which is changed to an MBSFN subframe, but do not find aframe in which CSI-RSs are aggregated to the subframe #4 or #9. That is,since this is not distinguished from the operation of the secondembodiment, the number of frames over which CSI-RSs are aggregated isseparately notified.

<Configuration and Operation of Base Station>

FIG. 12 is a block diagram showing the configuration of a base station500 in the third embodiment. The base station 500 is different from thebase station 100 of the first embodiment shown in FIG. 4 in that theoperations of a setting unit 501, a control unit 502, a CSI-RSgeneration unit 505, and a disposition unit 507 are different. Otherparts are the same as those in the first embodiment, and descriptionthereof will not be repeated.

The operation of the characteristic base station 500 in the thirdembodiment will be described. The setting unit 501 outputs settinginformation including CSI-RS disposition information at the normal time(normal mode) and during the execution of Extended Cell DTX (ExtendedCell DTX mode). The control unit 502 performs operation control relatingto CSI-RS transmission in each mode on the basis of the settinginformation from the setting unit 501. When changing from the normalmode to the Extended Cell DTX mode, the control unit 502 outputs controlinformation for reporting a subframe number to be changed to an MBSFNsubframe to the disposition unit 507, transmits the subframe number tobe changed to the MBSFN subframe and the number of frames over whichCSI-RSs are aggregated as the control signal of the upper-level layer,and gives notification to the terminal.

The CSI-RS generation unit 505 generates a CSI-RS on the basis of thesetting information input from the setting unit 501 at the normal timeand during the execution of Extended Cell DTX. At the normal time, thedisposition unit 507 orthogonally multiplexes CSI-RSs between thenearest cells in the same subframes from the subframes #1, #2, #3, #4,#6, #7, #8, and #9, and multiplexes CSI-RSs between other separate cellswith different subframes. During the execution of Extended Cell DTX, fora subframe which is changed to an MBSFN subframe, the disposition unit507 changes a CSI-RS from among CSI-RSs multiplexed to the subframes #1,#2, #3, #4, #6, #7, #8, and #9 to the subframe #4 or #9 and multiplexesthe CSI-RS over a plurality of frames while keeping relative CSI-RSmultiplex-disposition in the subframe.

<Configuration and Operation of Terminal (Mobile Station)>

FIG. 13 is a block diagram showing the configuration of a terminal 600in the third embodiment. The terminal 600 is different from the terminal200 of the first embodiment shown in FIG. 5 in that the operations of aseparation unit 605, a CSI-RS reception space information estimationunit 607, and a setting information reception unit 617 are different.Other parts are the same as those in the first embodiment, anddescription will not be repeated.

The operation of the characteristic terminal 600 in the third embodimentwill be described. The separation unit 605 acquires the control signalof the upper-level layer including the setting information from thesignal input from the FFT unit 204, and outputs the control signal tothe setting information reception unit 617. The setting informationreception unit 617 reads the setting information including the CSI-RSdisposition information from the control signal input from theseparation unit 605, and outputs the setting information to theseparation unit 605. The setting information reception unit 617 outputsthe setting information, such as a back-diffusion code for receiving anddemodulating a CSI-RS, to the CSI-RS reception space informationestimation unit 607.

The separation unit 605 separates the frequency domain signal input fromthe FFT unit 204 on the basis of the setting information received withthe previous subframes, acquires the CSI-RS, and outputs the CSI-RS tothe CSI-RS reception space information estimation unit 607. At thistime, the separation unit 605 acquires the CSI-RS in accordance withmapping of the CSI-RS to each subframe by the base station, and outputsthe CSI-RS to the CSI-RS reception space information estimation unit607.

At the normal time and during the execution of the Extended Cell DTX,the CSI-RS reception space information estimation unit 607 performsspace information estimation of the downlink transmitted from the basestation to the mobile station device itself by the CSI-RS input from theseparation unit 605 using the setting information of the CSI-RS inputfrom the setting information reception unit 617.

According to the third embodiment, the operation of the secondembodiment is partially changed, and CSI-RS mapping is expanded over aplurality of frames, thereby increasing the number of multiplexes ofCSI-RSs in a plurality of cells and multiplexing necessary CSI-RSs whilesecuring temporal orthogonality.

Although in the second embodiment and the third embodiment, when theExtended Cell DTX mode is not executed (the normal mode), descriptionhas been made assuming that CSI-RSs are transmitted with all subframesother than the subframes #0 and #5, actually, CSI-RSs may not betransmitted with all subframes capable of transmitting CSI-RSs. In thiscase, taking into consideration of having been changed to the ExtendedCell DTX mode, CSI-RSs are disposed and transmitted in advance asdescribed below.

(1): When transmitting a CSI-RS, first, the CSI-RS is transmittedpreferentially using the subframe #4 or #9. Only with the use of thesubframe #4 or #9, when the number of subframes is insufficient, CSI-RSsare transmitted using a necessary number of subframes from among othersubframes (#1 to #3 and #6 to #8). In this case, however, it is assumedthat, during the execution of the Extended Cell DTX mode, the change toFake MBSFN subframes is performed from subframes which do not transmitCSI-RSs.

(2): Similarly to (1), when transmitting a CSI-RS, the CSI-RS istransmitted preferentially using the subframe #4 or #9. When CSI-RSs aretransmitted at an interval of 20 ms or 40 ms in each cell, the CSI-RSsare transmitted with the subframe #4 or #9 of different frames for eachCSI-RS group. Similarly to (1), only with the use of the subframe #4 or#9, when the number of subframes is insufficient, CSI-RSs aretransmitted with other subframes, and it is assumed that the change toFake MBSFN subframes is performed from subframes which do not transmitCSI-RSs.

(3): Contrary to (1) or (2), when transmitting a CSI-RSs, the CSI-RS istransmitted preferentially using subframes (#1 to #3 and #6 to #8) otherthan the subframe #4 or #9. The change to Fake MBSFN subframes isperformed from subframes which do not transmit CSI-RSs from among thesubframes (#1 to #3 and #6 to #8), and thereafter, the change ofsubframes which transmit CSI-RSs is performed.

(4): Similarly to (3), when transmitting a CSI-RS, the CSI-RS istransmitted preferentially using subframes (#1 to #3 and #6 to #8) otherthan the subframe #4 or #9. The change to Fake MBSFN subframes isperformed from subframes which transmit the same number of CSI-RSs asthe subframe #4 or #9, and thereafter, the change of subframes which donot transmit CSI-RSs is performed.

Although in the foregoing embodiments, a case where CSI-RSs areaggregated to the subframes #4 and #9 incapable of acting as MBSFNsubframes and transmitted, the invention is not limited thereto, andother signals may be aggregated to the subframes #4 and #9. For example,the invention may be applied to a PDSCH, signaling of the upper-levellayer included in the PDSCH, or the like.

Even when the Extended Cell DTX mode is not executed, when a subframeacts as an MBSFN subframe, CSI-RSs or the like may be automaticallyaggregated to the subframe #4 or #9. Since the terminal does notdistinguish between real MBSFN subframes or Fake MBSFN subframes, in anycases, the base station just notifies the change to MBSFN subframes.

If the change to the Extended Cell DTX mode is possible, it isconsidered that the number of spatial multiplexes of a transmissionsignal may be small as much. For this reason, if unnecessary, eighttransmission antennas may be aggregated to four transmission antennas.In this case, since the number of usable subframes increases, it ispossible to increase the number of multiplexes of a CSI-RS in aplurality of cells.

The subframe interval may be changed from 10 and set to an interval of 3or 7 to change the transmission timing of CSI-RSs between adjacentcells. However, transmission is not performed with a subframecorresponding to BCH or SIB. In this case, interference to other cellsapplied to CSI-RSs becomes various patterns, and when averaging,measurement (line estimation, space information estimation, or the like)can be easily performed taking into consideration the influence of othercells.

It should be noted that one skilled in the art can make variousmodifications and changes based on the specification and the well-knowntechnology without departing from the gist and scope of the invention,which are also included in the invention to be protected. The respectiveconstitutional elements in the foregoing embodiments can be arbitrarilycombined without departing from the gist of the invention.

Although the foregoing embodiments, an antenna has been described, thesame may apply to an antenna port. An antenna port indicates a logicalantenna which is constituted by one or a plurality of physical antennas.That is, the antenna port is not limited as indicating a single physicalantenna, and may indicate an array antenna having a plurality ofantennas, or the like. For example, in LTE, while how many physicalantennas constitute the antenna port is not defined, a base station isdefined as a minimum unit for transmission of different referencesignals. The antenna port may be defined as a minimum unit inmultiplying the weight of a precoding vector.

In the embodiments, the cases in which the invention is realized byhardware have been described. However, the invention may be realized bysoftware.

Each functional block used to describe the embodiment and eachmodification is typically implemented by an LSI, which is an integratedcircuit. Each functional block may be integrated into one chip, or aportion of or the entire functional block may be integrated into onechip. Here, the LSI is used as the integrated circuit, but theintegrated circuit may be called an IC, a system LSI, a super LSI, or anultra LSI according to the degree of integration.

In addition, a circuit integration method is not limited to LSI, butcircuit integration may be implemented by a dedicated circuit or ageneral-purpose processor. After the LSI circuit is manufactured, aprogrammable FPGA (Field Programmable Gate Array) or a reconfigurableprocessor capable of reconfiguring the connection of circuit cells inthe LSI circuit or the setting thereof may be used.

When a circuit integration technique capable of replacing LSI appearswith the progress of semiconductor technology or other technologiesderived from the semiconductor technology, the technique may be used tointegrate the functional blocks. For example, biotechnology can beapplied.

This application is based on Japanese Patent Application (JapanesePatent Application No. 2010-137339) filed on Jun. 26, 2010, thedisclosure of which is incorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The invention has effects that the power saving effect can be maintainedand the transmission of an additional reference signal, such as aCSI-RS, can be enabled, and is useful for a wireless communicationdevice, a wireless communication method, or the like for performinginter-cell cooperative transmission/reception being studied in LTE-A,for example.

REFERENCE SIGNS LIST

-   100, 161, 162, 163, 300, 500: base station (cell)-   101, 301, 501: setting unit-   102, 302, 502: control unit-   104: CRS generation unit-   105, 305, 505: CSI-RS generation unit (reference signal generation    unit)-   106, 209: modulation unit-   107, 211, 307, 507: disposition unit-   108, 212: IFFT unit-   109, 213: CP addition unit-   110-1 to 110-M, 214-1 to 214-N: transmission RF unit-   111-1 to 111-M, 201-1 to 201-N: antenna-   112, 219: distribution unit-   151, 200, 400, 600: terminal-   171: macro cell-   202-1 to 202-N: reception RF unit-   203: CP elimination unit-   204: FFT unit-   205, 405, 605: separation unit-   206: CRS reception line estimation unit-   207, 407, 607: CSI-RS reception space information estimation unit    (space estimation unit)-   208: PDSCH reception unit-   210: DFT unit-   215: line quality information generation unit-   216: space information generation unit-   217, 417, 617: setting information reception unit-   218: aggregation unit-   220-1 to 220-N: RF block

The invention claimed is:
 1. A communication apparatus comprising: areceiver which, in operation, receives a downlink signal including aChannel State Information (CSI) reference signal mapped in a subframeother than subframes configured to be used for Multimedia Broadcastmulticast service Single Frequency Network (MBSFN) transmission, thesubframes including at least one subframe actually used for the MBSFNtransmission and another subframe reserved for the MBSFN transmission;and a transmitter which, in operation, transmits Channel QualityIndicator (CQI) information, the CQI information being estimated usingthe CSI reference signal.
 2. The communication apparatus according toclaim 1, wherein the CSI reference signal is mapped by multiplexing theCSI reference signal on a frequency region at at least one OrthogonalFrequency Division Multiplexing (OFDM) symbol.
 3. The communicationapparatus according to claim 1, wherein the CSI reference signal ismapped by multiplexing the CSI reference signal on a part of a pluralityof subcarriers of at least one Orthogonal Frequency DivisionMultiplexing (OFDM) symbol.
 4. The communication apparatus according toclaim 1, wherein the CSI reference signal is mapped by using two or moreOrthogonal Frequency Division Multiplexing (OFDM) symbols and bymultiplexing the CSI reference signal on a frequency region and a timeregion.
 5. The communication apparatus according to claim 1, wherein inthe subframe to which the CSI reference signal is mapped, a number ofsymbols on which the CSI reference signal is mapped is smaller than anumber of symbols on which a cell-specific reference signal (CRS) ismapped.
 6. A communication method comprising: receiving a downlinksignal including a Channel State Information (CSI) reference signalmapped in a subframe other than subframes configured to be used forMultimedia Broadcast multicast service Single Frequency Network (MBSFN)transmission, the subframes including at least one subframe actuallyused for the MBSFN transmission and another subframe reserved for theMBSFN transmission; and transmitting Channel Quality Indicator (CQI)information, the CQI information being estimated using the CSI referencesignal.
 7. The communication method according to claim 6, wherein theCSI reference signal is mapped by multiplexing the CSI reference signalon a frequency region at at least one Orthogonal Frequency DivisionMultiplexing (OFDM) symbol.
 8. The communication method according toclaim 6, wherein the CSI reference signal is mapped by multiplexing theCSI reference signal on a part of a plurality of subcarriers of at leastone Orthogonal Frequency Division Multiplexing (OFDM) symbol.
 9. Thecommunication method according to claim 6, wherein the CSI referencesignal is mapped by using two or more Orthogonal Frequency DivisionMultiplexing (OFDM) symbols and by multiplexing the CSI reference signalon a frequency region and a time region.
 10. The communication methodaccording to claim 6, wherein in the subframe to which the CSI referencesignal is mapped, a number of symbols on which the CSI reference signalis mapped is smaller than a number of symbols on which a cell-specificreference signal (CRS) is mapped.